Choline is conventionally obtained from biological sources with significant impurities and contaminants that are strong discolorants, noxious odor formers, and highly unstable to elevated temperatures. Choline, in the form of choline hydroxide, is most commonly obtained as a very impure viscous liquid with a dark color and strong odor caused from its impurities. These impurities are difficult to remove, even by distillation, and the synthesis of choline salts for industrial applications thus requires significant purification.
Synthesis of choline glycolate using purified glycolic acid reacted with choline hydrogen carbonate, which requires very pure choline hydrogen carbonate, is described by Constantinescu et al in Chem. Eng. Data, 52:1280-1285, 2007. Choline glycolate synthesis is also described by Fukaya et al (Green Chem., 9:1155-1157, 2007) wherein an anion exchange column is used to form choline hydroxide followed by addition of glycolic acid. This process requires a very pure, halogenated form of choline, and generates a halogenated waste stream that must be disposed of. These methods are labor intensive and expensive, and are not attractive for commercial-scale operations.
A need thus remains for a process for the high grade synthesis of a wide variety of choline salts that is capable of converting an inexpensive, impure, halogen-free source of choline.